Can I use primary domains for multiple target countries (using same language)?

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Background:

My primary market is UK, I also want to expand to US / Canada / Australia (English-Language countries)

In such case, whats the best domains solution for SEO & User experience? ( I use shopify payments to solve currency issue)

1, I use only Primary domain, like xxxx.com for all the English-Language countries.

2, I use subfolders , like XXXX, XXXX for different countries, even they use same launguage.

Thanks